1. Field of The Invention
This invention relates to a method for forming an electrode layer and more particularly, to a method for forming an Al layer by the use of a laser flow technique.
2. Description of The Prior Art
A typical known wiring method is described with reference to FIGS. 4 and 5 wherein FIGS. 4(a) and 4(b) are, respectively, illustrative views showing the formation steps using a laser flow technique and FIG. 5 shows a beam pattern in the laser flow process.
As is particularly shown in FIG. 4(a), a field oxide film 2 is formed on a non-active region of a Si substrate 1 by the LOCOS method. A gate electrode 3 is the formed on an active region of the Si substrate 1. Source and drain diffusion layers 4 are formed on the surface of the Si substrate 1 at opposite sides of the gate electrode 3. Subsequently, a BPSG film 5 serving as an intermediate insulation film is deposited over the entire surface of the Si substrate 1 on which the source drain diffusion layers have been formed. In order to permit contact with the source drain diffusion layers, contact holes 6 are formed through the BPSG film 5 by the RIE method. Over the entire surface of the BPSG film which has been provided with the contact holes 6, there are successively deposited by sputtering an Al-Si film 7 having a Si content of 1% and an amorphous Si film 8 used as an anti-reflective film. Since the films 7 and 8 are difficult to form in the contact holes 6 by sputtering, the film thicknesses become smaller than in other portions.
Thereafter, an XeCl excimer laser with a wavelength of 308 nm radiates over the IC chip formed on the Si substrate 1. The laser beam irradiation is effected by scanning or directing the beam having a given diameter in the manner shown in FIG. 5. At the time, the beam is projected or directed in such a way that when an adjacent portion is then irradiated, once irradiated portion of the IC chip is again irradiated with the beam in a next cycle at 10 to 50% of the beam size. In other words, while the beam is directed along one locus, it overlaps onto an adjacent path, which path will be more directly radiated at a later time, or will have already been irradiated.
As a result of the irradiation, the Al-Si film 7 flows to fully fill the contact holes 6 therewith as shown in FIG. 4(b). Subsequently, the Al-Si film 8 is subjected to patterning to form an Al wiring layer on the contact holes 6. It will be noted that during the metal flow (of film 7), the amorphous film 8 is molten in the Al-Si film.
In the case of the laser beam irradiation as set out above, it is necessary to superpose the laser beams every irradiation cycle wherein superposed portions of the respective IC chips suffer additional light energy as compared with portions where not irradiated twice by the superposition. In the superposed portions, the Al-Si film 7 abnormally grows with respect to the grain size. In a worst case, the Al-Si film 7 may be lost by evaporation or separation. Thus, the problem arises that the elements formed in the IC chip will be greatly damaged.
Moreover, since the amorphous Si film 8 is molten in the Al-Si film, there is the tendency that the resistance of the Al wiring 7 will increase, or Si nodules will increase in size and number. This leads to the problem that the wiring lifetime is considerably shortened.